Semiconductor light emitting device and method of producing the same

ABSTRACT

To provide a semiconductor light emitting device capable of improving an aspect ratio of a laser beam to make it close to a circular shape and a method of producing the same, a first conductive type first cladding layer  11,  an active layer  12,  and a second conductive type second cladding layer  17  having a ridge-shaped portion RD as a current narrowing structure are stacked on a substrate  10;  wherein the ridge-shaped portion includes a first ridge-shaped layer  15  on the side close to said active layer and having a high bandgap and a second ridge-shaped layer  16  on the side distant from the active layer and having a low bandgap, so that the semiconductor light emitting device is obtained. By using an epitaxial growth method, a first cladding layer, active layer and second conductive type second cladding layer are formed by being stacked on the substrate, a part of the second cladding layer is processed to be a ridge-shaped portion, and the second cladding layer is formed, so that the portion to be a ridge shape includes the first ridge-shaped layer and second ridge-shaped layer.

TECHNICAL FIELD

The present invention relates to a semiconductor light emitting deviceand a method of producing the same, and particularly relates to asemiconductor light emitting device with an improved beam shape and amethod of producing the same.

BACKGROUND ART

A semiconductor laser and other semiconductor light emitting device areused, for example, as a CD (compact disc) and DVD (digital versatiledisc), furthermore, a light source of an optical pickup device ofnext-generation optical disc devices and a light source of otherapparatuses in a variety of fields.

As the above semiconductor light emitting device, for example, asemiconductor laser made by an AlGaInP-based material is disclosed inthe non-patent article 1.

FIG. 1A is a sectional view of the semiconductor laser explained above.

For example, an n-type cladding layer 111 formed by an AlGaInP layer, anactive layer 112, a p-type cladding layer 117 formed by AlGaInP layers(113 and 115) and a p-type cap layer 118 formed by a GaAs layer areformed by being stacked on an n-type substrate 110 via a not shownn-type buffer layer.

An etching stop layer 114 of a GaInP layer is formed on a boundary faceof the AlGaInP layer 113 and the AlGaInP layer 115, and a portion from asurface of the p-type cap layer 118 to the AlGaInP layer 115 isprocessed to be a ridge (protrusion) shape RD so as to form a stripe asa current narrowing structure.

Current block layers 119 are formed on both sides of the ridge shape RDand, furthermore, a p-electrode 120 is formed to be connected to thep-type cap layer 118 and an n-electrode 121 is formed to be connected tothe n-type substrate 110.

FIG. 1B is a view of a bandgap profile of a section along x₁-x₂ in FIG.1A.

It shows a bandgap of each of the n-type cladding layer 111, activelayer 112, AlGaInP layer 113, etching stop layer 114 and AlGaInP layer115.

For example, a composition ratio of aluminum in the n-type claddinglayer 111 is 0.65, while that in both of the AlGaInP layers (113 AND115) is 0.70 and p-type cladding layers are configured to have a higherbandgap than that of the n-type cladding layer 111.

In the above semiconductor laser, to adjust an aspect ratio of the laserbeam and bring the beam shape close to a circular shape is one ofsignificant tasks.

The beam shape largely depends on a refractive index of each layercomposing the semiconductor laser.

On the other hand, in the conventional semiconductor laser explainedabove, a variety of attempts have been made to improve the internalquantum efficiency and two leakage currents are required to be minimum.

A first leakage current is a lateral direction leakage current I_(Lx),which leaks excessively in the X-direction parallel to a hetero junctionin the sectional view in FIG. 1. A second leakage current is alongitudinal direction leakage current I_(Ly) called an overflow,wherein electrons leak in the Y-direction from the active layer to thep-cladding layer.

There is a method of controlling the I_(Lx) by making a thickness of theAlGaInP layer 113 in FIG. 1 thin, however, it is actually difficult tomake the AlGaInP layer 113 thin by controlling to 300 nm or thinner.

For example, a difference of an effective refractive index N_(eff1) atthe center of the ridge stripe and an effective refraction indexN_(eff2) outside of the ridge stripe becomes large, light confinement inthe X-direction intensifies, a photon distribution at the center in theX-direction is maximized, and electron-hole consumption increases to beshort in supply. This is called hole-burning of carriers and photons areunable to be supplied with electron holes to maintain the mode at thistime, so that they tend to shift to a mode of receiving the supply. Thisphenomenon leads to a change of electron-light conversion efficiencythereof, and linearity of the light output—current (L-I) characteristicis deteriorated, which is observed as a phenomenon called kink.

Also, in the conventional semiconductor laser explained above, electronsleak as a longitudinal direction leakage current I_(Ly) from the activelayer to the p-type cladding layer due to the thermal electron energywhen at a high temperature and deterioration of the L-I characteristicsis caused.

As a nature of countermeasures thereof, a method of heightening a heightof an energetic barrier sensed by electrons belonging to a Γ-band and amethod of improving concentration of a p-type impurity of the claddinglayer have been general. At this time, it is known that a drift currentof an electron group belonging to an X-band increases when the AlGaInPlayer 113 is made thinner as a significant task (refer to the non-patentarticle 1).

This can be confirmed also by an experiment and the AlGaInP layer 113cannot be made very thin, so that a method of controlling the leakagecurrent I_(Lx) in the X-direction explained above cannot be used.

Non-Patent Article 1: Numerical Simulation of SemiconductorOptoelectronic Devices, proceedings, MD4, L39-40

Non-Patent Article 2: IEEE JQE, vol. 38, No. 3, March 2002, L285.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

A problem to be solved is a point that it is difficult to improve anaspect ratio of a laser beam to make it close to a circular shape in asemiconductor laser having the configuration shown in FIG. 1.

Means to Solve the Problem

A semiconductor light emitting device of the present invention comprisesa substrate; a first conductive type first cladding layer formed on thesubstrate; an active layer formed on the first cladding layer; and asecond conductive type second cladding layer formed on the active layer,a part thereof having a ridge-shaped portion as a current narrowingstructure; wherein said ridge-shaped portion of the second claddinglayer includes a first ridge-shaped layer on the side close to theactive layer and having a high bandgap and a second ridge-shaped layeron the side distant from the active layer and having a low bandgap.

In the above semiconductor light emitting device, a first conductivetype first cladding layer, an active layer and a second conductive typesecond cladding layer having a ridge-shaped portion as a currentnarrowing structure are stacked on a substrate. The second claddinglayer of the ridge-shaped portion is configured to include a firstridge-shaped layer on the side close to the active layer and having ahigh bandgap and a second ridge-shaped layer on the side distant fromthe active layer and having a low bandgap.

Also, a method of producing a semiconductor light emitting device of thepresent invention includes a step of forming at least a first conductivetype first cladding layer, an active layer and a second conductive typesecond cladding layer by stacking on a substrate by an epitaxial growthmethod; and a step of processing a ridge-shaped portion as a currentnarrowing structure at a part of the second cladding layer; wherein, inthe step of forming the second cladding layer, a portion to be saidridge-shaped portion is formed to include a first ridge-shaped layer onthe side close to the active layer and having a high bandgap and asecond ridge-shaped layer on the side distant from the active layer andhaving a low bandgap.

In the above method of producing a semiconductor light emitting deviceof the present invention, at least a first conductive type firstcladding layer, an active layer and a second conductive type secondcladding layer are formed by being stacked on a substrate by anepitaxial growth method and, next, a part of the second cladding layeris processed to be a ridge-shaped portion as a current narrowingstructure.

Here, when forming the second cladding layer, the portion to be theridge-shaped portion is formed to include a first ridge-shaped layer onthe side close to the active layer and having a high bandgap and asecond ridge-shaped layer on the side distant from the active layer andhaving a low bandgap.

EFFECT OF THE INVENTION

The semiconductor light emitting device of the present invention has theconfiguration that the ridge-shaped portion of the second cladding layerincludes a high bandgap layer and a low bandgap layer, consequently, theconfiguration that the ridge-shaped portion of the second cladding layerincludes a layer with a low refractive index and a layer with a highrefractive index is attained, so that a refractive index profile toaffect a beam shape of an emitted light can become adjustable and theaspect ratio of the beam can be improved to be close to a circularshape.

According to the method of producing the semiconductor light emittingdevice of the present invention, the ridge-shaped portion of the secondcladding layer is formed to include a high bandgap layer and a lowbandgap layer, so that a refractive index profile to affect a beam shapeof an emitted light can become adjustable and the aspect ratio of thebeam can be improved to be close to a circular shape.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1A is a sectional view of a semiconductor laser as asemiconductor light emitting device according to a conventional example,and FIG. 1B is a view of a bandgap profile on a section along x₁-x₂ inFIG. 1A.

[FIG. 2] FIG. 2A is a sectional view of a semiconductor laser as asemiconductor light emitting device according to a first embodiment ofthe present invention, and FIG. 2B is a bandgap profile on a sectionalong x₁-x₂ in FIG. 2A.

[FIG. 3] FIG. 3 is a schematic view for explaining an effect of reducingdrift electrons in the first embodiment of the present invention.

[FIG. 4] FIG. 4 is a view showing a result of measuring a thresholdcurrent of a semiconductor laser of an example and a comparative examplein example 1.

[FIG. 5] FIG. 5 is a view showing results of measuring θ⊥ of asemiconductor laser of an example and a comparative example in example2.

[FIG. 6] FIG. 6 is a view showing a result of measuring a differentialefficiency of a semiconductor laser of an example and a comparativeexample in example 3.

[FIG. 7] FIG. 7 is a view showing a result of measuring a kink level ofa semiconductor laser of an example and a comparative example in example4.

[FIG. 8] FIG. 8 is a view wherein a reduction rate KSEp of adifferential coefficient is plotted with respect to a half width θ// ofa far-field pattern.

[FIG. 9] FIG. 9A is a sectional view of a semiconductor laser as asemiconductor light emitting device according to a second embodiment ofthe present invention, and FIG. 9B is a view showing a bandgap profileon a section along x₁-x₂ in FIG. 9A.

EXPLANATION OF REFERENCES

10 . . . n-type substrate, 11 . . . n-type cladding layer (firstcladding layer), 12 . . . active layer, 13 . . . d2 layer, 14 . . .etching stop layer, 15 . . . d2′ layer (first ridge-shaped layer), 16 .. . second ridge-shaped layer, 17 . . . p-type cladding layer (secondcladding layer), 18 . . . p-type cap layer, 19 . . . current blocklayer, 20 . . . p-electrode, 21 . . . n-electrode, 110 . . . n-typesubstrate, 111 . . . n-type cladding layer, 112 . . . active layer, 113. . . AlGaInP layer p-type cladding layer, 114 . . . etching stop layer,115 . . . AlGaInP layer, 117 . . . p-type cladding layer, 118 . . .p-type cap layer, 119 . . . current block layer, 120 . . . p-electrode,121 . . . n-electrode

BEST MODE FOR CARRYING OUT THE INVENTION

Below, embodiments of a semiconductor light emitting device of thepresent invention will be explained with reference to the drawings.

First Embodiment

FIG. 2A is a sectional view of a semiconductor laser as a semiconductorlight emitting device according to the present embodiment.

For example, on an n-type substrate 10, an n-type cladding layer (firstcladding layer) 11 formed by an AlGaInP layer, an active layer havingthe multiquantum well structure, a d2 layer 13 formed by an AlGaInPlayer, an etching stop layer 14 formed by a GaInP layer, a d2′ layer(first ridge-shaped layer) 15 formed by an AlGaInP layer and a secondridge-shaped layer 16 formed by an AlGaInP layer are stacked via a notshown n-type buffer layer, wherein a portion from the d2 layer 13 to thesecond ridge-shaped layer 16 becomes a p-type cladding layer (secondcladding layer) 17. Furthermore, a p-type cap layer 18 formed by a GaAslayer is formed on the second ridge-shaped layer 16.

Also, a portion from a surface of the p-type cap layer 18 to the AlGaInPlayer 15 is processed to be a ridge (protrusion) shape RD to form astripe having a current narrowing structure, and a current block layer19 formed, for example, by AlInP, etc. is formed on both sides of theridge shape RD.

Also, a p-electrode 20 is formed to be connected to the p-type cap layer18, and an n-electrode 21 is formed to be connected to the n-typesubstrate 10.

FIG. 2B is a bandgap profile on the section along x₁-x₂ in FIG. 2A.

It shows a bandgap of each of the n-type cladding layer 11, active layer12, d2 layer 13, etching stop layer 14, d2′ layer (first ridge-shapedlayer) 15 and second ridge-shaped layer 16. Here, the height of thebandgap corresponds to the height of the composition ratio of aluminum,and the higher the composition ratio of aluminum is, the higher thebandgap becomes.

For example, a composition ratio of aluminum of the n-type claddinglayer 11 is 0.65, while in the p-type cladding layer, those of the d2layer 13 and d2′ layer (first ridge-shaped layer) 15 are 0.70 and thatof the second ridge-shaped layer 16 is 0.65. Namely, in the n-typecladding layer 11 and the p-type cladding layer 17, the profile is, forexample, bandgaps of the n-type cladding layer 11 and the secondridge-shaped layer 16 are low and bandgaps of the d2 layer and the d2′layer (first ridge-shaped layer) 15 are high.

As explained above, in the semiconductor laser of the presentembodiment, the ridge-shaped portion (d2′ layer (first ridge-shapedlayer) 15 and second ridge-shaped layer 16) of the p-type cladding layer(second cladding layer) 17 is configured to include the d2′ layer (firstridge-shaped layer) 15 with a high bandgap on the side close to theactive layer 12 and the second ridge-shaped layer 16 with a low bandgapon the side distant from the active layer 12.

Also, in the p-type cladding layer 17, the portion of the d2 layer 13and the d2′ (first ridge-shaped layer) 15 is configured to have a higherbandgap than that of the n-type cladding layer 11.

Also, the height of the aluminum composition ratio corresponds to theheight of the refractive index, and the higher the aluminum compositionratio is, the lower the refraction ratio is. Accordingly, the profileis, for example, refraction indexes of the n-type cladding layer 11 andthe second ridge-shaped layer 16 are high and those of the d2 layer 13and the d2′ (first ridge-shaped layer) 15 are low, that is, the d2′layer (first ridge-shaped layer) 15 is configured to be formed by alayer having the same refraction index as that of the d2 layer 13 as aportion excepting the ridge-shaped portion of the p-type cladding layer(second cladding layer) 17.

In a semiconductor laser as the semiconductor light emitting deviceaccording to the above present embodiment, as a result of applying apredetermined voltage to the p-electrode 20 and the n-electrode 21, alaser beam having a wavelength of, for example, 650 nm band is emittedfrom the laser beam emitting portion in the direction parallel to thesubstrate.

The above semiconductor laser may be an index guide and self pulsationtype, etc. by controlling a depth and shape, etc. of the ridge.

The semiconductor light emitting device according to the above explainedpresent embodiment has the configuration that the ridge-shaped portionof the p-type cladding layer (second ridge-shaped layer) includes a highbandgap layer and a low bandgap layer, consequently, the configurationthat the ridge-shaped portion of the second cladding layer includes alayer with a low refractive index and a layer with a high refractiveindex is attained, so that a refractive index profile to affect a beamshape of an emitted light can become adjustable, for example, a halfwidth (θ⊥) of a far-field pattern beam in the vertical direction withrespect to the hetero junction becomes small, and the aspect ratio ofthe beam can be improved to generate a beam pattern closer to a circularshape.

In the semiconductor laser of the present embodiment, it is preferablethat a composition ratio X1 of aluminum in the d2′ layer (firstridge-shaped layer) 15 satisfies 0.60≦X1≦0.70 and a composition ratio X2of aluminum in the second ridge-shaped layer 16 satisfies X2≦X1.

By attaining this configuration, a film thickness of the d2 layer 13 asa portion excepting the ridge-shaped portion of the p-cladding (secondcladding) layer having a high aluminum composition ratio can be made asthin as 50 to 350 nm, as a result, the current I_(Lx) leakingexcessively in the direction parallel to the hetero junction can bereduced.

As explained above, in the configuration of the present embodiment, as aresult that the ridge portion is configured to include the d2′ layer(first ridge-shaped layer) 15 as a low refractive index layer and thesecond ridge-shaped layer 16 as a high refractive index layer, even whenthe d2 layer 13 is made thin as 50 to 350 nm, a threshold current(threshold carrier density) of the semiconductor laser can be reduced,an overflow of electrons from the active layer to the p-side, which hasbeen a problem, can be suppressed, and the differential efficiency andkink level can be improved.

In the present embodiment, to correct the thinness of the d2 layer 13,the d2′ layer (first ridge-shaped layer) 15 having a high Al composition(0.60≦X1 0.70) is introduced, and the thickness can be made as thick as50 to 400 nm.

Theoretically, electrons overflowed from the active layer 12 may passthrough the d2 layer 13 via an X-band to rejoin at the etching stoplayer 14, while, a reduction of a threshold current value and animprovement effect of a temperature characteristic, etc. were observeddue to an effect of the d2′ layer (first ridge-shaped layer) 15 by wayof experiment.

In the case where the d2′ layer (first ridge-shaped layer) 15 having ahigh aluminum composition ratio is not formed, when the d2 layer 13 as aportion excepting the ridge-shaped portion of the p-cladding layer(second cladding layer) is made thin in order to aim the above effects,it is liable that an electron group belonging to the X-band passesthrough the d2 layer, acts as drift electrons, leaks to the p-typecladding layer and adversely leads to a deterioration of the temperaturecharacteristic (refer to the non-patent article 2).

FIG. 3 is a schematic view for explaining an effect of reducing driftelectrons in the present embodiment.

In the present embodiment, the ridge-shaped portion of the p-typecladding layer (second cladding layer) 17 is composed of the d2′ layer(first ridge-shaped layer) 15 having a high bandgap and the secondridge-shaped layer 16 having a low bandgap. The d2′ (first ridge-shapedlayer) 15 is provided not to contact with a SCH (Separate ConfinementHetero-structure) guide layer of the active layer 12 and the d2 layer 13and the etching stop layer 14 are provided between them, and it isconfirmed by way of experiment that the effect of suppressing the driftelectrons enhances as the thickness increases.

In an AlGaInP-based high-energy laser, a stripe width of a lower side ofthe trapezoidal ridge shape RD, a sectional view of which is as shown inFIG. 2A, has to be as narrow as 2.5 μm or less to improve the kinklevel. However, it is technically difficult to make the ridge shapeupright and, when the stripe width of the lower side becomes narrow, theupper side of the ridge trapezoid becomes extremely narrow to cause anew disadvantage that the resistance becomes high.

In the semiconductor laser structure according to the presentembodiment, the d2′ layer (first ridge-shaped layer) 15 in the figurehas a high Al composition on average than that in the secondridge-shaped layer 16 formed above it. Therefore, in a wet etching stepfor producing the ridge shape in the figure, an etching rate of the d2′layer (first ridge-shaped layer) 15 becomes faster than that of thesecond ridge-shaped layer 16.

Consequently, etching proceeds faster at the lower portion of the ridgeshape RD, so that the stripe width of the lower side can be madenarrower by 0.2 μm or so comparing with that in the case of producingthe same upper side. Namely, the ridge shape can be more uprightcomparing with that in the conventional cases, so that the kink levelimproves.

From the above reason, a film thickness of the d2 layer 13 is preferably50 to 350 nm or so. When it exceeds 350 nm, the current ILx leakingexcessively in the direction parallel to the hetero junction increases,which is unfavorable.

Also, a sum of film thicknesses of the d2 layer 13 and the d2′ (firstridge-shaped layer) 15 is preferably 750 nm or smaller. When exceeding750 nm, θ⊥ of the beam declines.

Also, a film thickness of the d2′ (first ridge-shaped layer) layer 15 ispreferably 50 to 400 nm or so. This is for the sum of film thicknessesof the d2 layer 13 and the d2′ (first ridge-shaped layer) 15 not toexceed 750 nm as explained above.

EXAMPLE 1

A semiconductor laser having the configuration shown in FIG. 2 wasproduced as an example by following the above embodiment, and asemiconductor laser having the configuration shown in FIG. 1 wasproduced as a comparative example. A threshold current was measured onboth of the semiconductor lasers.

The results are shown in FIG. 4.

A lower threshold current was obtained in the semiconductor laser of theexample than that of the comparative example.

EXAMPLE 2

In the same way as in the example 1, a semiconductor laser as an exampleand that as a comparative example were produced, a far-field pattern inthe vertical direction with respect to the hetero junction was observedon both of the semiconductor lasers and the θ⊥ was measured.

The results are shown in FIG. 5.

A smaller θ⊥ value was obtained in the semiconductor laser as theexample than that of the comparative example.

EXAMPLE 3

In the same way as in the example 1, a semiconductor laser as an exampleand that as a comparative example were produced, and a differentialefficiency was measured on both of the semiconductor lasers.

The results are shown in FIG. 6.

A larger differential efficiency value was obtained in the semiconductorlaser as the example than that of the comparative example.

EXAMPLE 4

In the same way as in the example 1, a semiconductor laser as an exampleand that as a comparative example were produced, a kink level (100 ns,70° C.) was measured on both of the semiconductor lasers.

The results are shown in FIG. 7.

The kink level was improved in the semiconductor laser as the examplecomparing with that in the comparative example.

EXAMPLE 5

In the same way as in the example 1, a semiconductor laser as an exampleand that as a comparative example were produced, and a reduction rateKSEp of a differential coefficient of the L-I curve and a half width θ//of a far-field pattern as an indication of light confinement of a lightin the X-direction were measured on both of the semiconductor lasers.The larger the KSEp value is, the higher the tortuosity of L-I (arisingof kink) is.

FIG. 8 is a view wherein reduction rates KSEp of differentialcoefficients is plotted with respect to the half width θ// (output of 5mW) of a far-field pattern.

In the comparative example, when the half width θ// of the far-fieldpattern is large, kink easily arises along with the hole burning effect.

In the example, the kink level does not decline even when the half widthθ// of the far-field pattern becomes large.

This also contributes to an improvement of the aspect ratio of the beamto generate a more circular beam pattern as explained above, and themerit is significant in an optical disk application.

EXAMPLE 6

In the same way as in the example 1, a semiconductor laser as an exampleand that as a comparative example were produced, and an operationcurrent value during an operation at a high temperature was measured onboth of the semiconductor laser.

The semiconductor laser as the example exhibited a smaller operationcurrent value in high temperature operation comparing with that of thecomparative example.

A method of producing the semiconductor laser according to the presentembodiment as above will be explained.

For example, by using an epitaxial growth method, such as an organicmetal vapor epitaxial growth method (MOVPE), a not shown buffer layer,the n-type cladding layer (first cladding layer) 11 formed by an AlGaInPlayer, the active layer 12, the d2 layer 13 formed by an AlGaInP layer,the etching stop layer 14 formed by a GaInP layer, the d2′ layer (firstridge-shaped layer) 15 formed by an AlGaInP layer, the secondridge-shaped layer 16 formed by an AlGaInP layer and the p-type caplayer 18 formed by a GaAs layer are stacked in order on the n-typesubstrate 10. Here, a portion from the d2 layer 13 to the secondridge-shaped layer 16 becomes the p-type cladding layer (second claddinglayer) 17.

Here, film formation is performed, so that, for example, a compositionratio of aluminum in the n-type cladding layer 11 is 0.65, those of thed2 layer 13 and d2′ layer (first ridge-shaped layer) 15 as p-typecladding layers are 0.70, and that of the second ridge-shaped layer 16is 0.65.

Namely, in a step of forming the p-type cladding layer (second claddinglayer) 17, a layer having the same refraction index as that of a portionexcepting the ridge-shaped portion of the second cladding layer isformed as the d2′ (first ridge-shaped layer) 15.

Next, for example, AlInP, etc. is stacked allover the surface to form acurrent block layer 19, and a contact opening is formed, so that thep-type cap layer 18 is exposed.

Next, the p-electrode 20 made by Ti/Pt/Au, etc. is formed to beconnected to the p-type cap layer 18, and the n-electrode 21 made byAuGe/Ni/Au, etc. is formed to be connected to the n-type substrate 10.

After that, through a pelletizing step, a desired semiconductor laser asshown in FIG. 2A can be obtained.

In the method of producing the semiconductor light emitting device ofthe present embodiment, since the ridge-shaped portion of the secondcladding layer is formed to include a layer with a high bandgap and alayer with a low bandgap, the configuration that the ridge-shapedportion of the second cladding layer includes a layer with a lowrefractive index and a layer with a high refractive index is attained,so that a refractive index profile to affect a beam shape of an emittedlight can become adjustable and the aspect ratio of the beam can beimproved to be close to a circular shape.

In the above embodiment, an AlGaInP-based semiconductor light emittingdevice is explained, but the present embodiment is not limited to thatand may be applied to an AlGaN-based semiconductor light emittingdevice.

The layer composition and the configuration can be same as those in theAlGaInP-based case in FIG. 2A. In this case, it is preferable that analuminum composition ratio X1 of the d2′ layer (first ridge-shapedlayer) is 0.05≦X1≦0.20 and an aluminum composition ratio of layers, suchas the second ridge-shaped layer, other than the d2′ layer (firstridge-shaped layer) is X2≦0.20. As a result, the same effects as thosein the case of the AlGaInP-based semiconductor light emitting device canbe obtained.

Second Embodiment

FIG. 9A is a sectional view of a semiconductor laser as a semiconductorlight emitting device according to the present embodiment.

A semiconductor laser according to the present embodiment has the sameconfiguration as that in the first embodiment. For example, on an n-typesubstrate 10, an n-type cladding layer (first cladding layer) 11 formedby an AlGaInP layer, an active layer 12 having the multiquantum wellstructure, a d2 layer 13 formed by an AlGaInP layer, an etching stoplayer 14 formed by a GaInP layer, a d2′ layer (first ridge-shaped layer)15 formed by an AlGaInP layer and a second ridge-shaped layer 16 formedby an AlGaInP layer are stacked via a not shown n-type buffer layer,wherein a portion from the d2 layer 13 to the second ridge-shaped layer16 becomes a p-type cladding layer (second cladding layer) 17.Furthermore, a p-type cap layer 18 formed by a GaAs layer is formed onthe second ridge-shaped layer 16.

Also, a portion from a surface of the p-type cap layer 18 to the AlGaInPlayer 15 is processed to be a ridge (protrusion) shape RD to form astripe having a current narrowing structure, and a current block layer19 formed, for example, by AlInP, etc. is formed on both sides of theridge shape RD.

Also, a p-electrode 20 is formed to be connected to the p-type cap layer18, and an n-electrode 21 is formed to be connected to the n-typesubstrate 10.

FIG. 9B is a bandgap profile on the section along x₁-x₂ in FIG. 9A.

It shows a bandgap of each of the n-type cladding layer 11, active layer12, d2 layer 13, etching stop layer 14, d2′ layer (first ridge-shapedlayer) 15 and second ridge-shaped layer 16. Here, the height of thebandgap corresponds to the height of the aluminum composition ratio, andthe higher the aluminum composition ratio is, the higher the bandgapbecomes.

In the semiconductor laser of the present embodiment, an aluminumcomposition ratio X0 of the d2 layer 13, an aluminum composition ratioX1 of the d2′ layer (first ridge-shaped layer) 15, and an aluminumcomposition ratio X2 of the second ridge-shaped layer 16 as aridge-shaped portion other than the d2′ layer (first ridge-shaped layer)15 satisfy X2<X0<X1. An aluminum composition ratio of the n-typecladding layer 11 is made equal to the aluminum composition ratio of thesecond ridge-shaped layer 16.

For example, the aluminum composition ratio in the n-type cladding layer11 is 0.65, while in the p-type cladding layer, that in the d2 layer 13is 0.68, that of the d2′ layer (first ridge-shaped layer) 15 is 0.75 to0.80 and that in the second ridge-shaped layer 16 is 0.65.

Namely, the n-type cladding layer 11 and the p-type cladding layer 17has a profile that, for example, a bandgap is low in the n-type claddinglayer 11 and the second ridge-shaped layer 16, a bandgap is high in thed2 layer 13, and a bandgap in the d2′ layer (first ridge-shaped layer)15 is still higher.

The semiconductor layer of the present embodiment is configured that theridge-shaped portion (the d2′ layer (first ridge-shaped layer) 15 andsecond ridge-shaped layer 16) of the p-type cladding layer (secondcladding layer) 17 includes a d2′ layer (first ridge-shaped layer) 15 onthe side close to the active layer 12 and having a high band gap and asecond ridge-shaped layer 16 on the side distant from the active layer12 and having a low bandgap.

Also, a portion of the d2 layer 13 and the d2′ layer (first ridge-shapedlayer) 15 in the p-type cladding layer 17 is configured to have a higherbandgap than that of the n-type cladding layer 11.

Also, the height of the refraction index corresponds to the height ofthe aluminum composition ratio, and the higher the aluminum compositionratio, the lower the refractive index becomes.

Accordingly, with the above aluminum composition profile, a refractionindex profile, that a refraction index of the n-type cladding layer 11and that of the second ridge-shaped layer 16 are high, that of the d2layer 13 is low and that of the d2′ layer (first ridge-shaped layer) 15is still lower, is obtained in the n-type cladding layer 11 and thep-type cladding layer 17.

Accordingly, the d2′ layer (first ridge-shaped layer) 15 is configuredto be composed of a layer with a lower refractive index than that of thed2 layer 13 as a portion excepting the ridge-shaped portion of thep-type cladding layer (second cladding layer) 17.

Other than the above, the semiconductor laser of the present embodimentis substantially the same as that in the first embodiment.

In the semiconductor laser as a semiconductor light emitting deviceaccording to the present embodiment explained above, by applying apredetermined voltage to the p-electrode 20 and the n-electrode 21, alaser beam having a wavelength of, for example, 650 nm band is emittedfrom the layer light emitting portion in the direction parallel to thesubstrate.

The above semiconductor laser may become an index guide and selfpulsation type, etc. by controlling a depth and shape of the ridge.

The semiconductor light emitting device according to the presentembodiment as above has the configuration that the ridge-shaped portionof the p-type cladding layer (second cladding layer) includes a highbandgap layer and a low bandgap layer, consequently, the configurationthat the ridge-shaped portion of the second cladding layer includes alayer with a low refractive index and a layer with a high refractiveindex is attained, so that the refractive index profile to affect on thebeam shape of the emitted light becomes adjustable, for example, thehalf width (θ⊥) of the far-field pattern beam in the vertical directionwith respect to the hetero junction becomes small, and the aspect ratioof the beam can be improved to generate a more circular beam pattern.

Particularly, as explained above, when with the refractive index profilethat the refractive index of the n-type cladding layer 11 and that ofthe second ridge-shaped layer 16 are high, that of the d2 layer 13 islow, and that of the d2′ layer (first ridge-shaped layer) 15 is stilllower, a light distribution in the laser longitudinal direction can bedesigned at a higher degree of freedom, moreover, by adjusting thealuminum composition ratio of the second ridge-shaped layer 16 and filmthicknesses of the d2 layer 13 and the d2′ layer (first ridge-shapedlayer) 15 and adjusting aluminum composition ratios of the di2 layer 13and the d2′ layer (first ridge-shaped layer) 15, the light distributioncan be optimized and a spot of a laser beam to be emitted can be madecloser to a perfect circle.

In the semiconductor laser according to the present embodiment, it isalso preferable, as in the same way as in the first embodiment, a filmthickness of the d2 layer 13 is 50 to 350 nm or so, a film thickness ofthe d2′ layer (first ridge-shaped layer) 15 is 50 to 400 nm or so, and asum of film thicknesses of the d2 layer 13 and the d2′ layer (firstridge-shaped layer) 15 is 750 nm or smaller.

The semiconductor laser according to the present embodiment is capableof attaining the configuration that the aluminum composition ratio ofthe d2′ layer (first ridge-shaped layer) 15 is furthermore higher thanthat in the first embodiment. Here, the higher the aluminum compositionis, the faster the etching rate of processing a ridge shape, so that theetching rate ratio thereof to the etching stop layer 14 can be increasedand it is possible to make the ridge shape more upright when processingthe ridge shape comparing with that in the first embodiment, so that thekink level improves. Also, etching unevenness on a wafer surface of thecladding can be suppressed.

The semiconductor laser according to the present embodiment can beproduced in the same way as that in the first embodiment by forming asthe first ridge-shaped layer a layer having a lower refractive indexthan that of a portion excepting the ridge-shaped portion of the secondcladding layer in the step of forming the second cladding layer.

The present invention is not limited to the above explanations.

For example, the present invention can be applied to an AlGaAs-basedsemiconductor light emitting device other than an AlGaInP-based andAlGaN-based semiconductor light emitting devices.

Other than that, a variety of modifications may be made within the scopeof the present invention:

INDUSTRIAL APPLICABILITY

The semiconductor light emitting device of the present invention can beapplied as a CD and a DVD, moreover, a light source of an optical pickupdevice of a next-generation optical disc apparatus and a light source ofother apparatuses in a variety of fields.

The method of producing the semiconductor light emitting device of thepresent invention can be applied as a method for producing a CD and aDVD, moreover, a light source of an optical pickup device of anext-generation optical disc apparatus and a light source of otherapparatuses.

1. A semiconductor light emitting device, comprising: a substrate; afirst conductivity type first cladding layer on said substrate; anactive layer on said first cladding layer; and a second conductivitytype second cladding layer on said active layer, a part thereof having aridge-shaped portion as a current narrowing structure, wherein, saidridge-shaped portion of said second cladding layer includes a firstridge-shaped layer on the side closest to said active layer and having ahigher bandgap than said first cladding layer and a second ridge-shapedlayer on the side distant from the active layer and having a relativelylow bandgap, said first ridge-shaped layer and said second ridge-shapedlayer are a layer with a relatively high aluminum composition ratio anda layer with a relatively low aluminum composition ratio, respectively,an aluminum composition ratio X1 of said first ridge-shaped layer is0.60<X1<0.70, and an aluminum composition ratio X2 of said secondridge-shaped layer is X2<X1.
 2. A semiconductor light emitting device asset forth in claim 1, wherein: an aluminum composition ratio X1 of saidfirst ridge-shaped layer is 0.70, and an aluminum composition ratio X2of said second ridge-shaped layer is 0.65.
 3. A semiconductor lightemitting device as set forth in claim 1, wherein a film thickness ofsaid first ridge shaped layer is 50 to 400 nm.
 4. A semiconductor lightemitting device as set forth in claim 1, wherein a sum of a filmthickness of a portion excepting said ridge-shaped portion of saidsecond cladding layer and a film thickness of said first ridge-shapedlayer is 750 nm or smaller.
 5. A semiconductor light emitting device asset forth in claim 1, wherein an etching stop layer is on a boundaryface of a portion excepting the ridge-shaped portion of said secondcladding layer and said first ridge-shaped layer.
 6. A semiconductorlight emitting device as set forth in claim 1, wherein said firstcladding layer, said active layer and said second cladding layercomprises an AlGaInP-based material.
 7. A semiconductor light emittingdevice as set forth in claim 1, wherein said first cladding layer, saidactive layer and said second cladding layer comprises an AlGaN-basedmaterial.
 8. A semiconductor light emitting device as set forth in claim1, wherein said first ridge-shaped layer comprises a layer having anequal refractive index to that of a portion excepting said ridge-shapedportion of said second cladding layer.
 9. A semiconductor light emittingdevice as set forth in claim 1, wherein said first ridge-shaped layercomprises a layer having a lower refractive index than that of a portionexcepting said ridge-shaped portion of said second cladding layer.
 10. Asemiconductor light emitting device as set forth in claim 9, wherein analuminum composition ratio of said portion excepting said ridge-shapedportion of said second cladding layer is 0.68, and an aluminumcomposition ratio of said first ridge-shaped layer is 0.75 to 0.80. 11.A method of producing a semiconductor light emitting device, including:a step of forming at least a first conductivity type first claddinglayer, an active layer and a second conductivity type second claddinglayer by stacking on a substrate by an epitaxial growth method; and astep of processing a ridge-shaped portion as a current narrowingstructure at a part of said second cladding layer, wherein, in the stepof forming said second cladding layer, a ridge-shaped portion is formedto include a first ridge-shaped layer on the side close to said activelayer and having a higher bandgap than said first cladding layer and asecond ridge-shaped layer on the side distant from the active layer andhaving a relatively low bandgap, in the step of forming said secondcladding layer, a layer having a relatively high aluminum compositionratio and a layer having a relatively low aluminum composition ratio areformed as said first ridge-shaped layer and said second ridgeshapedlayer, respectively, and in the step of forming said second claddinglayer, a layer having an aluminum composition ratio X1 satisfying0.60<X1<0.70 is formed as said first ridge-shaped layer and a layerhaving an aluminum composition ratio X2 of X2<X1 as said secondridge-shaped layer.
 12. The method of producing a semiconductor lightemitting device as set forth in claim 11, wherein in the step of formingsaid second cladding layer, a layer having an aluminum composition ratioX1 of 0.70 is formed as said first ridge-shaped layer and a layer havingan aluminum composition ratio X2 of 0.65 is formed as said secondridge-shaped layer.
 13. The method of producing a semiconductor lightemitting device as set forth in claim 11, wherein in the step of formingsaid second cladding layer, said first ridge-shaped layer is formed tohave a film thickness of 50 to 400 nm.
 14. The method of producing asemiconductor light emitting device as set forth in claim 11, wherein inthe step of forming said second cladding layer, a sum of a filmthickness of a portion excepting said ridge-shaped portion of saidsecond cladding layer and a film thickness of said first ridge-shapedlayer is made to be 750 nm or smaller.
 15. The method of producing asemiconductor light emitting device as set forth in claim 11, wherein inthe step of forming said second cladding layer, an etching stop layer isformed on a boundary face of a portion excepting said ridge-shapedportion of said second cladding layer and said first ridge-shaped layer.16. The method of producing a semiconductor light-emitting device as setforth in claim 15, wherein in the step of processing said ridge-shapedportion as the current narrowing structure at the part of said secondcladding layer, the part of said second cladding layer is processed tobe said ridge-shaped portion by etching which stops at said etching stoplayer.
 17. The method of producing a semiconductor light-emitting deviceas set forth in claim 11, wherein said first cladding layer, said activelayer and said second cladding layer are formed by of AlGaInP-basedmaterial.
 18. The method of producing a semiconductor light emittingdevice as set forth in claim 11, wherein said first cladding layer, saidactive layer and said second cladding layer are formed by of AlGaN-basedmaterial.
 19. The method of producing a semiconductor light emittingdevice as set forth in claim 11, wherein in the step of forming saidsecond cladding layer, a layer having a same refractive index as that ofa portion excepting said ridge-shaped portion of said second claddinglayer is formed as said first ridge shaped layer.
 20. The method ofproducing a semiconductor light emitting device as set forth in claim11, wherein in the step of forming said second cladding layer, a layerhaving a lower refractive index than that of a portion excepting saidridge-shaped portion of said second cladding layer is formed as saidfirst ridge shaped layer.
 21. The method of producing a semiconductorlight emitting device as set forth in claim 20, wherein in the step offorming said second cladding layer, a layer having an aluminumcomposition ratio of 0.68 is formed as a portion excepting saidridge-shaped portion of said second cladding layer and a layer having analuminum composition ratio of 0.75 to 0.80 is formed as said firstridge-shaped layer.